biomass co-firing

Why RWE is backing biocoal

1 August 2008

Biomass but not as we know it...

Using torrefaction – a form of pyrolysis in which biomass is heated to 320°C without oxygen – combined with pelletisation, Dutch start-up company Topell is planning to produce a new form of biomass fuel, “biocoal” pellets (pictured above).

These torrefied pellets have a very high energy density compared with conventional biomass-derived pellets and a number of other properties, including better combustion properties, which make them more coal like and better suited to biomass co-firing applications. In particular they can be burned together with coal in conventional power plants without requiring any further infrastructure provisions such as separate storage or crushing. They are also easier to transport. In the Topell process, the biomass partially decomposes (in particular the hemi-celluloses), losing its fibrous structure and giving off volatiles including the remaining moisture.

Topell’s plan is to build a commercial facility for producing the pellets next year, in the Netherlands. The plan received a boost recently with the announcement that RWE has taken a 25% stake in the company.

Prof Fritz Vahrenholt, CEO of RWE Innogy, explained: “With our venture engagement with Topell, we have secured access at a very early stage to a technology that effectively reduces CO2 emissions in conventional power plants and the associated financial burdens. Once a successful test run of the first commercial plant has been completed, we therefore plan to expand production...”

RWE Innogy says the investment in Topell is an example of its policy of investing in “highly promising young technology enterprises, decisively contributing towards the development of future technologies in Europe,” with priority “given to financing fledgling companies in the start-up or growth phase and providing equity capital or financial resources similar to equity capital.” For 2008, a budget of r50 million has been earmarked for this purpose and RWE Innogy describes the Topell investment as its “first transaction in the venture capital business.”

Topell has a target production capacity of 1 million t by 2012 – about 3-5% of the estimated global biopellet market by then.

Flexible process

The process developed by Topell can be applied to a wide variety of organic materials, including just about all fibrous biomasses, not just wood. Even comparatively difficult and low value biomass, such as roots and switch grass, can be converted into high value biocoal pellets through torrefaction and pelletisation using the reactor technology developed by Topell, the company says. Organic waste flows as well as cultivated biomass can be used as the pellets produced are, with the exception of ash content, homogeneous.

The process uses the Torbed reactor system developed by Polow Energy Systems, also of the Netherlands. Among the advantages of the the Torbed reactor are:

• Highly efficient heat transfer. The turbulence inside the reactor causes intense contact between the biomass and the process air, thus facilitating good heat transfer rates. This, in combination with the small bed volume, provides excellent control of the process within small limits inside the reactor.

• Good heat recycling and heat recovery. By recycling a large amount of the process air when drying the biomass, large energy savings are achieved.

• No moving parts in the reactor. As the functioning of the Torbed reactor is completely based on the displacement of air, it does not feature any moving parts inside its reactor chamber, resulting in very low maintenance costs.

The production process is extremely flexible in terms of raw material inputs, making it unnecessary to call upon biomass resources that might also be used as foodstuffs.

Biocoal benefits

Compared with conventional wood pellets, Topell claims the following advantages for its biocoal pellets: energy density of 18-20 GJ/m3 compared with 10-11 GJ/m3; homogeneous not heterogeneous; hydrophobic not hydrophilic; no biological activity as opposed to some biological activity; easy to grind instead of hard to grind; and little smoke production instead of average smoke production.

Since the increased energy density of biocoal pellets reduces transport costs per GJ by almost 50% in comparison with conventional pellets the torrefaction process adds most value close to the biomass source, Topell argues. Therefore the company says it is looking for partnerships with companies and/or organisations who can deliver a long term supply of suitable biomass.

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